FR2647379A1 - METHOD AND DEVICE FOR FEEDING LIQUID METAL FROM A MOLD - Google Patents

Abstract

A mould containing a gasifiable consumable pattern 3, embedded in a binder-free sand, is fed via its base by a pressurised chamber 6 containing liquid cast iron, the pressure in the chamber 6 being regulated as a function of the surface/volume ratio of the consumable pattern 3. <??>Application to the elimination of bright carbon.

Description

The present invention relates to a method and

  a liquid metal supply device of a mold.

  The present invention more particularly relates to a method and a feed device ferrous alloy, a mold consisting of a gasifiable lost model embedded in an unbound granular molding material, which

  suppresses the appearance of the brilliant carbon phenomenon.

  In installations of this type, a gasifiable lost model made of expanded polystyrene is used at each casting. This model, once produced, is covered with a refractory coating and placed in the actual mold where it is embedded in a granular material,

  usually sand, which is compacted by vibrating.

  The mold is then made and can be fed with liquid metal which then vaporizes the lost gasifiable model. This process is known under the general name

full mold casting.

  In the case of realizations of ferrous alloy parts with high melting points such as cast iron or steel, the material constituting the lost model is not always fully vaporized. In addition it frequently happens that the constituents of the lost model, which have been vaporized in a

  first time, partially recondensent afterwards.

  In both cases, residues are formed

  carbonaceous on the surface of the molded part.

  In the case of low carbon parts, such as steels, carbon residues dissolve in

the liquid metal.

  Nevertheless, even in this case, the consequences are not negligible since there appears in the piece a carbon content gradient, the surface of the

  room is richer in carbon than the body of the room.

  Thus, the guaranteed low carbon steel parts could not be manufactured to date

  the solid mold casting process described above.

  In the case of high-carbon metal parts such as ductile cast iron

are even more important.

  In fact, what is classically called brilliant carbon appears and is manifested randomly in the form of discontinuities in the thickness and irregularities on the surface of the molded part which are harmful

to the health of the room.

  Thus, until now, there was no method and device allowing a simple and reproducible way to manufacture ductile iron parts having high mechanical characteristics in the context of the solid mold process with gasystable expanded polystyrene lost model or any other material

  which breaks down by producing carbon residues.

  To overcome the appearance of brilliant carbon and the diffusion of carbon in the molded part, it has been

  proposed to change the material constituting the lost model.

  Thus, in place of polystyrene, polymethyl methacrylate appeared which, when it is subjected to pyrolysis in the temperature range of the ferrous alloys, evaporates completely while not producing

no carbon residues.

  But, if this product avoids the appearance of carbon

  brilliant, it presents other problems.

  Indeed, besides the problem of its price, it appears to be less solid than polystyrene, which requires an increase in precautions when handling the model, and, moreover, it generates a greater quantity of gas which can cause a delivery of the liquid metal during feeding of the mold, which

  requires doubling the filling time of the mold.

  The present invention therefore aims to solve

the problems above.

  The present invention more particularly relates to a method and a device for producing ferrous alloy parts by the solid mold casting process, in which the gasifiable lost model is made of a material producing carbon residues in the range of casting of this ferrous alloy, which eliminate the problems related to the production of these carbon residues by suppressing the appearance of brilliant carbon. The features and benefits will emerge from

  following description which will follow made reference

  to the accompanying drawings given by way of non-limiting example and among which: FIG 1 represents a mold casting installation

  solid operating according to the method according to the invention.

  FIG. 2 represents the pressure regulation circuit

according to the invention.

  The applicant has discovered that, under certain conditions, the use of a liquid mold feed plant of the type described in document FR-A-2,295,808 makes it possible to avoid the appearance of the

brilliant carbon.

  Thus, as illustrated in FIG. 1, the plant operating according to the method according to the invention comprises a liquid iron feed installation 1 intended to supply a mold 2 consisting of a gasifiable lost model 3 embedded in a sand without

  binder 4 inside a box 5.

  The installation 1 comprises a chamber 6 under pressure of gas inside which is located the

  liquid cast iron for feeding the mold 2.

  This enclosure 6 comprises a cover 7 sealingly attached to the enclosure 6, a pouring nozzle 8 passing through an orifice 9 the cover 7, the junction between the nozzle 8 and the cover 7 being sealed. This nozzle 8 is traversed, vertically and from one side, by a dip tube 10 which is immersed in the molten iron

  to the vicinity of the floor of the enclosure 6.

  The enclosure 6 is connected, by a circuit 12, to a source of pressurized gas 11 constituted by an enclosure

fed with pressurized gas.

  The gasifiable bleedable model 3, made of expanded polystyrene, comprises two parts, a part 13 corresponding to the shape of the part to be produced and a part 14 constituting the casting well through which the liquid metal then feeds the attacks of the

piece to realize.

  This gasifiable lost model 3 is positioned by its part 14 in an orifice 15 formed in an insert 16 made of refractory material, this insert 16 being fixed in a removable manner in an opening 17 formed at the base of the

box 5.

  As can be seen in FIG. 1, the pouring nozzle 8, by its upper end, is intended to come into contact by sealing contact against the insert 16 of the frame 5, the tube

  plunger 10 communicating with the orifice 15 of the insert 16.

  Orifices 18 are formed in the side walls 19 of the box 5 to connect this box 5 to a

  vacuum device not shown.

  As can be seen in FIG. 2, the circuit 12 has a regulating device 20 constituted by one or more solenoid valves which control the communication between the enclosure 6 and the source of pressurized gas 11. The regulation device 20 is connected to a calculator that continuously compares the existing pressure in

  the enclosure 6 with a set pressure.

  Between the regulating device 20 and the enclosure 6 is placed a gas reservoir 21 which acts as a buffer capacity, connected to the enclosure 6 by a conduit 22 of large diameter, this reservoir 21 having a leak 23

permed.

  The method according to the invention and the implementation of the operating device will now be described.

  according to the process according to the invention.

  According to the conventional operation of a casting installation such as that described in document FR-A-2 295 808, the nozzle 8 is applied in a sealed manner against the insert 16 of the box 5 on the lower face of

this one.

  Subsequently, the pressure chamber 6 containing the molten iron has its pressure P increase at a certain speed dP / dT (T representing the time) so that the liquid iron contained in the chamber rises in the tube diver and enters the box 5

  through the orifice 15 of the insert 16 at a certain flow rate.

  The lost model 3 then vaporizes under the action of the heat of the liquid iron injected into the mold 2

  as the mold 2 fills.

  It is at this stage of filling of the mold 2 that, in

  the prior art, the phenomenon of shiny carbon appears.

  However, the plaintiff discovered without being able to explain that, by regulating the feed rate of the

  liquid metal mold, the above phenomenon disappears.

  Indeed, the Applicant has discovered that the optimum feed rate of the cast iron mold to obtain a piece of o shiny carbon is excluded is a function of the geometry of the gasifiable lost model and more particularly of its ratio S / V, S being the

  lost model surface and V its volume.

  It appears in fact that the lower the S / V ratio, the more brilliant carbon appears, all things being equal, but if the feed rate of the mold is increased to a certain value the

phenomenon disappears.

  The method according to the present invention therefore consists in producing a ductile iron piece in a mold consisting of a lost model of expanded polystyrene embedded in a sand without a binder, the mold being fed with liquid iron at its base by a feed device consisting of a pressure vessel containing the molten iron, wherein the feed rate of the cast iron mold is calculated according to the S / V ratio of the gasifiable lost model so that the phenomenon of

bright carbon does not appear.

N> 2647379

  It is necessary for this to obtain a perfect regulation of the pressure inside the chamber 6 that no previous device allowed. This is what the regulating device 20 allows. Indeed, when it is desired to regulate the pressure inside a ladle, the temperatures reached by the gases in said ladle make it necessary to move the solenoid valves away from the ladle. in order to prevent the seals of the solenoid valves from burning during the pressure drop phases that occur once

the mold is filled.

  This results in a time constant that impairs the

  stability of the pressure regulation.

  However, thanks to the gas reservoir 21 which acts as a buffer capacity, the pressure is in fact regulated by the solenoid valves in said reservoir 21 which communicates with the pressure vessel 6 via a conduit 22 of the bulk

  diameter which limits the pressure losses.

  Thus, the tank 21 allows the gases from the chamber 6 to cool to an acceptable temperature

  for the operation of the solenoid valves.

  Furthermore, another problem of regulation results from the fact that the gases introduced into the enclosure 6 are heated in it, which causes the enclosure to increase the undesirable pressure after

stopped injecting the gas.

  Thanks to the permanent leak 23 which is formed on the tank 21, which acts as a buffer capacity, the system is permanently maintained in admission during

  all the phases of filling of the mold 2.

  The facts set out above are demonstrated by the

numerical examples that follow.

  For the production of a valve body of 17 kg of cast iron weight in a full mold fed by a casting installation as described above, the liquid cast iron in the bag being at a temperature between 1420 C and 1460 C, mold feed rates of 1 kg / s and 3.3 kg / s gave defective parts while a flow of 5.7 kg / s allowed to obtain a part

perfectly healthy.

  This illustrates that, by regulating the pressure in the feed bag and thus the feed rate in a full mold process, a part can be obtained.

  made of ductile iron where the bright carbon is excluded.

  Moreover, for the production of a 2.1 kg exhaust manifold it was possible to obtain a sound part with a feed rate of 3.3 kg / s, which illustrates that the optimal flow rate is a function of the

  geometry of the piece and thus the gasifiable lost model.

  The above invention is applicable in the same way to both a mold for the production of a single piece that a mold for the realization of several parts. In the latter case, the gasifiable lost model consists of several parts, corresponding to the different parts to be produced, placed in

  cluster after the well 14.

2647379 '

Claims (5)

  1.- A process for producing a ductile iron piece in a mold (2) consisting of a gasifiable lost model (3), made of a material producing carbon residues in the casting temperature range of the cast iron, embedded in a sand (4) without binder, characterized in that the mold (2) is fed with liquid iron at its base by a feed device consisting of a chamber (6) under pressure containing the liquid iron, the flow rate of supply of the cast iron mold (2) is regulated by the pressure prevailing in the chamber under pressure so that the carbon phenomenon brilliant does not appear.   2. A process according to claim 1 characterized in that the pressure in the enclosure (6) under pressure is regulated according to the S / v ratio of the gasifiable lost model (3), S representing the surface of the model lost (3) and V its volume.   3. A process according to claim 2 characterized in that the pressure of the chamber (6) under pressure is controlled by changing the pressure in a buffer capacity constituted by a reservoir (21) under pressure   connected to said enclosure (6) under pressure.   4.- Pressure regulating device for the   implementation of the method according to one of the claims   previous characterized in that a buffer capacity constituted by a reservoir (21) is interposed between a device (20) of pressure regulation and the chamber (6) - 5.- Device according to claim 4 characterized in that the reservoir ( 21) constituting the buffer capacity   has a permanent leak (23).   6.- Device according to claim 4 characterized in that the reservoir (21) constituting the buffer capacity is connected to the enclosure (6) under pressure by a conduit (22) large diameter.